Background: Encephalitis is associated with significant mortality and morbidity, but its cause remains largely unknown. We designed a national prospective study in France in 2007 to describe patients with encephalitis, investigate the etiologic diagnosis of encephalitis, and assess risk factors associated with death.
Methods: Patients were enrolled by attending physicians according to case definition, and data were collected with a standardized questionnaire. The etiologic diagnosis was investigated after a standardized procedure. Risk factors associated with death during hospitalization were assessed by multivariate logistic regression.
Results: A total of 253 patients with acute infectious encephalitis from 106 medical units throughout France were included in the study. Their ages ranged from 1 month to 89 years (median age, 54 years); 61% were male. Cause of the encephalitis was determined in 131 patients (52%). Herpes simplex virus 1 (42%), varicella-zoster virus (15%), Mycobacterium tuberculosis (15%), and Listeria monocytogenes (10%) were the most frequently identified agents. Twenty-six patients (10%, all adults) died, 6 of them with tuberculosis and 6 with listeriosis. Risk factors independently associated with death during hospitalization identified by the multivariable analysis were age (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.0-1.4; for 5-year increase), cancer (OR, 17; 95% CI, 2.3-122.6), immunosuppressive treatment before onset (OR, 24; 95% CI, 1.3-426.0), percentage of hospitalized patients receiving mechanical ventilation (OR, 2.0; 95% CI, 1.4-3.0; for 10% increase), the etiologic agent, coma on day 5 after admission (OR, 16; 95% CI, 2.8-92.3), and sepsis on day 5 after admission (OR, 94; 95% CI, 4.9-1792.2).
Conclusions: Our prospective study provides an overview of the clinical and etiologic patterns of acute infectious encephalitis in adults in France. Herpes simplex virus 1 remains the main cause of encephalitis, but bacteria accounts for the highest case-fatality rates.